I've never used live sand: it's ok to use, she says reluctantly, if it really is alive. If it smells like rotten eggs when you open the bag, don't use it. Personally, I use medium grade aragonite. A new sandbed, if connected to an old tank with a mature dsb, will set up in a couple of weeks or less...but rock, which is harder to permeate, won't. THat's why I consider live sand kind of a waste: you're going to have to take the extra time to let the rock 'set up', so why pay extra for live sand? By the time your rock has set up, dry sand has become 'live sand,' anyway.
To start with all live rock, 1-2 lbs per gallon, takes about 4 weeks to set up. And live sand just cannot shove bacteria deeper into that rock any faster, no matter what. Bacteria have to work their own way inward, and the 'right kind' of bacteria have to multiply.
Now if you're dealing with live rock that's been live and submerged in a working tank as late as yesterday, and kept submerged in a bucket (as in, say, a house move) you might see a small cycle in as little as 5 days. If you do it tank to tank inside your house, you might see hardly any cycle at all, if you start with your old sand well-washed, and I emphasize---very well washed in salt water, until the water runs clear. This would get out all the crud and leave only the bacteria.
If, however, you are starting from scratch, I recommend dry sand, and live rock, and if all live rock, it takes about 4 weeks. For a 30 gallon tank, that's between 100-200.00 worth of rock; for a 90 gallon, well, that's 300-600.00 worth of rock. BUT if you get base rock, ie, dry holey limestone or old dry dead coral, you're going to spend far less, if you're lucky, a couple of dollars a pound. That means your 30 gallon tank is going to use 60.00 worth of rock, and your 90 gallon tank is 150 worth of rock instead of 600.00. Use 10% really good rock, with a lot of creepy crawlies, and give it 8 to 12 weeks to cycle, then a month of letting hermits and snails working it over before adding your first (quarantined) fish, and you've gotten the equivalent of the priciest rock going, if you just treat it gently and way understock for the first 3 months of its career. Most of the creepy crawlies will survive a cycle, and help it along a little besides, with their poo, though with the 10% live setup, I would suggest that you feed the tank about 5 flakes of fish food per 50 gallons during the cycling process. This will give the creepy crawlies a better chance of survival.
It's a tradeoff. But live rock sources are getting fewer, the collection may damage reefs, and personally, I prefer to minimize getting live rock out of the wild.
